As a technique of associating body parts information and a system with each other in a tomograph, Japanese Patent Laid-Open No. 3-224545 discloses a tomograph which moves an X-ray tube and film in synchronized with each other and performs tomography on a predetermined slice of an object to be radiographed. The tomograph comprises a distance measurement means which is arranged near the X-ray tube and measures the distance to the surface of an object, and a control means which obtains the object thickness from the measured distance and automatically sets a radiographing condition from the object thickness and a set a body part to be radiographed. The radiographing condition is an X-ray exposure condition.
Many modifications to the tomograph are disclosed in Japanese Patent Laid-Open No. 10-295680. Tomographs include one in which the detector is not always moved but is fixed and only the tube is moved, and one in which only an object to be radiographed is moved without moving the detector and tube. By moving the object, the detector and tube for which it is difficult to control need not be moved in synchronized with each other, avoiding degradation in the image quality of a tomographic image caused by synchronous control. In addition, a complicated control mechanism and control circuit for synchronous control can be omitted, reducing the manufacturing cost of the tomograph.
Also in an X-ray stereography and apparatus disclosed in Japanese Patent Laid-Open No. 2000-237177, an-X-ray detector 14 is fixed, and only the X-ray tube is moved. In this moving method, the X-ray tube need not move around an object to be radiographed. The X-ray stereogram of a patient can be obtained while he/she is standing as if he/she were taking fluoroscopy of chest. Unlike a conventional X-ray CT apparatus, the necessity for ensuring a space where the X-ray tube moves or the necessity for a mechanism which conveys a patient into the apparatus while keeping him/her laid can be obviated. The installation area of the apparatus can, therefore, be greatly reduced.
Japanese Patent Registration No. 03149268 discloses various types of imaging apparatuses for forming dental slice images. For example, in type A, both the X-ray generator and X-ray detection surface are moved without moving the support with respect to a slice. In type B, the support is linearly moved parallel to the slice, and at least either the X-ray generator or X-ray detection surface is moved. In type B, only the X-ray detection surface is moved without moving the X-ray generator with respect to the support, like type C, or only the X-ray generator is moved with respect to the support without moving the X-ray detection surface, like type D.
As described above, in the conventional tomograph, an X-ray tube and detector for tomography, and efficient motion of an object to be radiographed are disclosed. However, the X-ray tube, detector, and object are not moved in accordance with the body part to be radiographed.
The tomograph radiographs various body parts with various radiographing sizes. If the detector is moved without considering the size of the body part to be radiographed, the movable portion of the apparatus becomes unnecessarily large, and a wide operating range must be ensured.
A large moving amount takes a long time for positioning a movable portion, decreasing the radiographing efficiency.
When a wide radiographing range is ensured, a body part other than the original body part to be radiographed also exposes to X-rays, which is not preferable in term of reduction in the influence on a human body.